1. Field of the Invention
The present invention relates generally to a centrifugal acceleration tester, and more particularly to a turntable type acceleration generating apparatus applicable for examining characteristics of an acceleration sensor for sensing an acceleration, e.g., force, acceleration, and magnetism, which is capable of reducing noise generated during the measurement for examining characteristics of an acceleration sensor or reducing noise, i.e., undesirable acceleration generated due to the drive torque of a servo motor for a rotating small-diameter turntable.
2. Related Art
The following control is widely conducted. Force, acceleration, magnetism of an object moving in a three dimensional space, e.g., robots and air planes, and another object moving in two-dimensional space, e.g., motor vehicles, are sensed by an acceleration sensor. Motions of the object or various devices carried on the object are controlled in accordance with the thus gathered data, for intended purposes. Various types of acceleration sensors are currently used for this type of control. It is necessity to know the characteristics of the acceleration sensors before the sensors are assembled into the control devices.
A vibration tester is currently used for examining the characteristics of the acceleration sensor. The examining method using the vibration tester has the following problems, however.
1) The method examines an acceleration characteristic of an object to be examined, i.e., an acceleration sensor, in a manner that the object is located on a testing table and subjected to a reciprocative acceleration. The testing table somewhat slants during the reciprocative operation (vertical vibration) of the testing table. The table slanting makes it difficult to secure an exact reciprocative motion. Where the table slants, a force component is additionally applied to the acceleration sensor under test in the directions different from those of the reciprocative forces. The resultant of the measurement includes an interference component in addition to an acceleration of the sensor. The interference component contained in the measurement result impairs the examination of the characteristics of the acceleration sensor in examination exactness.
2) In the vibration tester, the acceleration sensor actually vibrates by use of a vibration generator. Therefore, the test per se is inevitably large in scale. Further, it is necessary to actually apply a dynamic acceleration of vibration to the acceleration sensor. This results in complexity of the testing procedure.
For this background, the inventors of the present Patent Application proposed the solution to the problems. The solution takes the form of a centrifugal acceleration tester capable of remarkably improving the testing accuracy in Japanese Patent Laid-Open Publication No. Hei. 7-110342. In the tester, an object to be tested, i.e., a acceleration sensor, is placed on a testing table, and a predetermined acceleration (i.e., a DC component of acceleration) is applied to the object, whereby the characteristics of the acceleration sensor are examined with high precision.
FIG. 5 is a schematic illustration of the centrifugal acceleration tester. As shown, a signal line 51 is used for deriving an acceleration signal from a sensor table placed on the turntable. A control signal line 52 feeds a control signal to the servo motor to drive the sensor table for its turn. The signal line 51 and the control signal line 52 are gathered together and located on one of the sides (usually the underside) of the turntable, and a coupling ring 53 is applied to the bundle of the lines. In the wiring, noise derived from the control signal line 52 to the servo motor leaks into the signal line 51, viz., it is superposed on a signal traveling through the signal line 51 as shown in FIG. 6. The actual use of the acceleration test showed the fact that this noise makes it difficult to exactly measure the characteristics of the acceleration sensor.
In addition, when the small-diameter turntable is turned to examine the characteristics of the acceleration sensor by use of the centrifugal acceleration tester, an acceleration is generated by a starting torque of the servo motor. This acceleration serves as noise to thereby deteriorate an accuracy of the measurement. In measuring the characteristics of the acceleration sensor, the small-diameter turntable needs to shift its operation mode from a non-rotation mode to a rotation mode by the drive of the second servo motor. At this time, friction resistance of the bearing, weight of the small-diameter turntable, and other factors cause a starting torque. This starting torque serves as noise to deteriorate an accuracy of the measurement for examining the characteristics of the acceleration sensor.